Children with cardiac arrest (CA) have mortality rates of 50-90%, largely due to neurological failure as part of the post-resuscitation syndrome. There is a critical gap of knowledge and tools to accurately classify outcome after pediatric CA. Physical examination and laboratory testing inadequately assess the severity of neurologic injury and outcome. Hazards of misclassification include risking adverse effects from ineffective therapies and non-treatment of ostensibly well patients who later are found to have neurologic deficits. Early and accurate identification of the eventual severity of neurologic injury would allow for timely neuroprotective interventions and/or more targeted testing of new therapies in specific risk populations. The long term objective is to improve the neurological outcome of children surviving CA. In this study, investigators will model and validate serum and imaging biomarkers of brain injury with empirical support, and assess their accuracy together with clinical variables in classifying outcome after pediatric CA. The central hypothesis is that serum and imaging biomarkers of brain injury, together with clinical variables, will critically aid in the early classification of favorable outcome after pediatric CA (Vineland Adaptive Behavior Scales score [VABS] > 70) 1 year after pediatric CA in a multicenter prospective study (8-12 centers and 248 subjects). Strong preliminary data supports this hypothesis, and biomarkers will be tested for outcome classification accuracy in the following 3 specific aims: